<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box{width: 100px;height: 100px;background-color: aqua;}
    </style>
</head>
<body>
    <div id="box"></div>
    
</body>
<script>
    var box =document.getElementById("box")

    // box.onclick = function(){
    //     console.log(1)
    // }

    box.onclick = fn();
    function fn(){
        console.log(2)
    }

    // box.onclick = function(){
    //     fn();
    // }
    // function fn() {
    //     console.log(3)
        
    // }


    






</script>
</html>